Two honest and bold police officers Adhi Narayanan (Kamal Hassan) and Abbas (Arjun) device a master plan to bring in control the Terrorist Groups and send two secret vigilance officers, named Anand and Shiva on an operation called Operation "Dhanush". The objective is to infiltrate a terror group headed by a man named Badri, and send information back to Abbas. A leak from inside the police camp leads the terrorist to oust Anand as a spy but before they could torture him and get the information of the second spy, he commits suicide.

Through Shiva, Adhi and Abbas learn of the arrival of an RPG expert shooter into the city to assassinate a minister who is to arrive soon. Adhi and Abbas manage to corner the RPG shooter in a railway station but he manages to escape the police in an intense shoot out. The police duo captures the driver (Nasser) of the car that had come to pick up the shooter.

Thus starts the mind game between Adhi and the Driver. Adhi tortures the driver for information on the terrorist head Badri and the spy inside the police camp but the driver maintains his innocence. Adhi, convinced that the driver holds a mid-level position in the terrorist camp, refuse to believe him.

Meanwhile, Adhi and Abbas change the route of the minister who was to be assassinated at the last minute. But the terrorist knew about this plan and the RPG shooter kills the minister but is then captured by the police. The shooter identifies Srinivasan, a senior police officer who was Adhi’s mentor, as the spy who had alerted the terrorists of the change of plan. Before he can be arrested, Srinivasan commits suicide, after confessing to Adhi that he was threatened by the terrorist group that they would kill his family if he didn’t act as a spy. This enrages Adhi and he beats up the driver even more.

The driver then used one of his men inside the prison he is kept in to pass instructions to kill Adhi’s pet to show Adhi that he can kill Adhi’s family just as easily. The Driver reveals himself as Badri, the head of the terrorist group and threatens to kill Adhi’s family if he is not let go. Adhi, manages to let Badri escape. Adhi acts as the new spy for the terrorist group. Abbas gets a little suspicious and follows Adhi when he goes to meet Badri. Abbas is caught, tortured and killed.

Overcome with sadness, Abbas’s wife Geetha and their teenage daughter come to live with Adhi, his wife, Sumitra (Gautami) and their son. Badri, again threatens Adhi to let a couple of terrorists come and live with him to keep a closer eye on Adhi. Overcome with guilt and grief over Abbas’s death and his betrayal of his duty, he realizes that he is travelling down the same path Srinivasan had done and decides to end the arrangement.

Adhi manages to find the safe house the terrorists reside in. Meanwhile, the terrorist staying at Adhi’s house tries to rape Abbas’s teenage daughter. Gautami, intervenes and offers herself to him instead. While he gets a bit too excited, she gets the gun off him and kills him.

As Adhi approaches the safe house, he is captured and the roles are reversed as Badri tortures Adhi to reveal the information of the second spy in the terrorist’s camp. When only Adhi, Badri and Badri’s second in command, Shiva is left in the room, Badri reveals to Adhi that the group has even found the radio used by the spy and that Danush (the codename of the spy) can no longer contact the police. This surprises Adhi and he looks at Shiva, who is the spy, for confirmation. Badri notices this and realizes that Shiva is Dhanush. Adhi breaks free and tussle with Badri when Badri tries to kill Shiva. This leads to a tussle in which Adhi kills Badri.

Adhi, who believes that the mission to bring down all the terrorist organizations is more important than his life, insists Shiva to shoot him so that Shiva could continue being the spy. Shiva shoots and kills Adhi just as the other terrorist members enter the room hearing the commotion inside. Shiva convinces the others that Badri was killed by Adhi and he killed Adhi. He proclaims that as Badri is dead, he, the second in command, will take over the reins of the group.

The story shows its ending as the beginning of a new era with the sons of Adhi and Narasimha confronting each other.